Recent data suggests the spinal cord of tetrapod vertebrates may be organized into circuits that control forcefield primitives. Recent data from my laboratory shows the temporal dynamics of primitives in spinalized frogs appear to have constant duration in many contexts, including rapid on-line trajectory corrections. We hypothesize this time scale is a conserved characteristic of the spinal circuits. If correct, this time scale defined by a primitive would impact on spinal trajectory formation, motor learning and the partitioning of control between spinal and supraspinal systems. To test the hypothesis in detail we have three specific aims: (1) We will test the hypothesis that all adjustments of trajectory formation in spinal wiping reflex can be understood as regulation of phase and amplitude of primitives but not the duration or temporal dynamics. (2) We will test the hypothesis that individual and ensemble sensory feedback circuits acting on force-field primitives are organized to preserve the temporal dynamics of primitives. (3) We will test how descending controls from medulla and tegmentum recruit and/or reorganize the timing properties of spinal primitives to build adaptable motor behaviors. Our data will bear on trajectory formation at the spinal level, interaction of descending and spinal motor control circuits, neural reorganization, design of neural repair and rehabilitation strategies following injury, design of neuroprostheses, and biomorphic robotics.